Method for Decoding a Video Signal

ABSTRACT

A method for efficiently decoding a video signal is disclosed. The method for decoding a video signal based on fine granularity scalability (FGS) includes obtaining a first reference picture from a reference picture list, decoding a current block using the first reference picture, wherein the first reference picture and a second reference picture corresponding thereto have the same picture identification information and are distinguished from each other by another identification information. Accordingly, it is possible to minimize a problem caused in a procedure for decoding a video signal due to transmission error.

TECHNICAL FIELD

The present invention relates to a method for decoding a video signal.

BACKGROUND ART

A communication environment is currently being changed together with thedevelopment of a Broadband convergence Network (BcN) for allowing aservice such as a wired and wireless complex network, a combination of abroadcasting network and a communication network, or IP convergenceusing an Internet protocol (IP) network. Such a tendency for change ofthe communication environment will be accelerated in future. Due to thechange of the communication environment, terminals used in a variety ofcommunication environments are being diversely changed and processingcapabilities of the terminals are also being changed. Accordingly, inorder to provide video signals optimized for various communicationenvironments and various terminals, a variety of video signals providedto the terminals must be created. In order to provide the optimizedvideo signals to the terminals, one video source must include a varietyof combinations of variables such as the number of transmission framesper second, resolution and the number of bits per pixel, etc. Thisimposes a great burden on content providers.

In view of the above, the content providers encode an original videosignal into high-bitrate compressed video data, decode the compressedvideo data into the original video signal when a request for the videois received from a terminal, and encode the original data into videodata suitable to a video processing capability of the terminal beforeproviding the video data to the terminal. However, in such transcoding(a combination of decoding and encoding), processes of encoding,decoding and encoding must be performed and thus a time delay occurswhen providing the video signal to the terminal. Therefore, a devicehaving complex hardware and algorithms is further required.

In order to solve such a problem, a scalable video coding (SVC) has beensuggested. This method can represent video signals by encoding the videosignals into a sequence of pictures with highest image quality anddecoding only a part (a partial sequence of pictures intermittentlyselected from total sequence of frames) of the sequence of pictures. Thesequence of pictures encoded using the SVC can reduce a video size usingspatial scalability or reduce image quality using SNR scalability with alow bitrate. At this time, a sequence of pictures having a small screensize and/or a small number of frames per second is referred to as a baselayer and a sequence of pictures having a large screen size and/or alarge number of frames per second is referred to as an enhanced orenhancement layer.

Although it is possible to represent video signals in low image qualityby receiving and processing a part of the sequence of pictures encodedin the scalable method as described above, the image quality issignificantly degraded as the bitrate is lowered. One solution to thisproblem is to provide an auxiliary picture sequence having low bitrates,for example, a sequence of pictures that have a small screen size and/ora small number of frames per second. The auxiliary picture sequence isreferred to as a base layer, and a main picture sequence is referred toas an enhanced (or enhancement) layer.

In this SVC, if a part of enhanced layer bitstream is lost when decodinga specific picture including the enhanced layer, which is encoded andtransmitted, a decoder decodes the picture using the lost enhanced layerbitstream. Accordingly, the image qualities of the original videosignals and the decoded video signals are different from each other.Specifically, when the picture having the above-mentioned problem is areference picture necessary for decoding the other pictures as well as akey picture, the problem becomes more severe.

DISCLOSURE OF INVENTION

Accordingly, the present invention is directed to a method for decodinga video signal that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention devised to solve the problem lies ona decoding method which is capable of minimizing a problem caused in aprocedure for decoding a video signal due to transmission error.

Another object of the present invention devised to solve the problemlies on a method for managing a decoded picture buffer according to adecoding method which is capable of minimizing a problem caused in aprocedure for decoding a video signal due to transmission error.

The object of the present invention can be achieved by providing amethod for decoding a video signal based on fine granularity scalability(FGS) comprising: obtaining a first reference picture from a referencepicture list; decoding a current block using the first referencepicture, wherein the first reference picture and a second referencepicture corresponding thereto have the same picture identificationinformation and are distinguished from each other by anotheridentification information.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a schematic block diagram of a scalable video coding system towhich the present invention applies;

FIG. 2 is a view showing a structure of pictures used in a decodingmethod and a method for managing a decoded picture buffer according toan embodiment of the present invention;

FIG. 3 is a flowchart illustrating a method for decoding a video signalaccording to an embodiment of the present invention;

FIG. 4 is a flowchart illustrating a method for decoding a video signalaccording to another embodiment of the present invention;

FIG. 5 is a view illustrating a structure of a decoded picture bufferaccording to an embodiment of the present invention;

FIGS. 6 a to 6 b are views illustrating reordering of reference numbersof a reference picture according to an embodiment of the presentinvention;

FIG. 7 is a view illustrating management contents of a decoded picturebuffer corresponding to code numbers of a memory management controloperation (MMCO); and

FIG. 8 is a view illustrating a structure of a decoded picture bufferaccording to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

In addition, although the terms used in the present invention areselected from generally known and used terms, some of the termsmentioned in the description of the present invention have been selectedby the applicant at his or her discretion, the detailed meanings ofwhich are described in relevant parts of the description herein.Furthermore, it is required that the present invention is understood,not simply by the actual terms used but by the meanings of each termlying within.

FIG. 1 is a schematic block diagram of a scalable video coding system towhich the present invention applies.

The scalable video coding system includes an encoder 2 and a decoder 10.The encoder 2 includes a base layer encoder 4, an enhanced layer encoder6 and a mux 8. The decoder 10 includes a demux 12, a base layer decoder14 and an enhanced layer decoder 16. The base layer encoder 4 compressesan input video signal X(n) and generates a base layer bitstream. Theenhanced layer encoder 6 generates an enhanced layer bitstream using theinput video signal X(n) and information generated by the base layerencoder 4 and the mux 8 generates a scalable bitstream using the baselayer bitstream and the enhanced layer bitstream. The generated scalablebitstream is transmitted to the decoder 10 via a certain channel and thetransmitted scalable bitstream is divided into the enhanced layerbitstream and the base layer bitstream by the demux 12 of the decoder10. The base layer decoder 14 receives the base layer bitstream anddecodes the base layer bitstream into an output video signal Xb(n), andthe enhanced layer decoder 16 receives the enhanced layer bitstream anddecodes the enhanced layer bitstream into an output video signal Xe(n).The output video signal Xb(n) has lower resolution and image qualitythan the output video signal Xe(n).

FIG. 2 is a view showing a structure of pictures used in a decodingmethod and a method for managing a decoded picture buffer according toan embodiment of the present invention.

In the structure of pictures, a Group of Picture (GOP) is formed of ahierarchical B picture structure, and pictures which configure the GOPare classified into key picture and non-key picture. One pictureconsists of a base layer reference picture QB and an enhanced layerreference picture QE. The key picture represents a picture having alowest temporal level and the non-key picture represents pictures exceptthe key picture.

In this structure, a current picture may use at least one picture fromthe pictures having temporal levels lower than or equal to that of thecurrent picture as a reference picture. For example, when a firstpicture 22 is an I picture encoded by an intra prediction, the firstpicture 22 is decoded without a reference picture, a second picture 24is decoded using the first picture 22 as the reference picture, a thirdpicture 26 is decoded using the first and second pictures 22 and 24 asthe reference pictures, fourth pictures 28 and 30 are decoded using thefirst and third pictures 22 and 26 or the second and fourth pictures 24and 26 as the reference pictures, fifth pictures 32, 34, 36 and 38 aredecoded using the first and fourth pictures 22 and 28, the third andfourth pictures 26 and 28 or the second and fourth pictures 24 and 30 asthe reference pictures. The pictures are decoded in order of the firstpicture 22, the second picture 24, the third picture 26, the fourthpictures 28 and 30, and the fifth pictures 32, 34, 36 and 38. The firstand second pictures 22 and 24 are the key pictures and the third tofifth pictures 26, 28, 30, 32, 34, 36 and 38 are the non-key pictures.The key picture includes the base layer reference picture and theenhanced layer reference picture and is represented as the first picture22 and the second picture 24 in FIG. 2. When the non-key picture is usedas the reference picture, the enhanced layer reference picture of thenon-key picture is referred. The enhanced layer reference picture of thenon-key picture indicates that the base layer reference picture of thenon-key picture is already reconstructed, and is represented by a dottedline, as the third to fifth pictures 26, 28, 30, 32, 34, 36 and 38 shownin FIG. 2.

FIG. 3 is a flowchart illustrating a method for decoding a video signalaccording to an embodiment of the present invention.

First, the decoder receives the encoded video signal via a certainchannel. Picture identification information indicating a referencepicture of a current block is acquired from the video signal (S310). Thepicture identification information may be, for example, reference indexinformation or picture number information of the reference picture. Thecurrent block may be decoded using the reference picture (S320). Thebase layer reference picture and the enhanced layer reference picturecorresponding thereto may have the same picture identificationinformation. The picture identification information may be the referenceindex information or the picture number information of the referencepicture. The enhanced layer reference picture may have an image qualityhigher than that of the base layer reference picture.

When the picture including the current block is the key picture, thereference picture of the current block may be the base layer referencepicture or the enhanced layer reference picture corresponding thereto.The reference picture of the current block may be obtained from areference picture list based on the picture identification information.The current block can be decoded using the obtained reference picture.Even in this case, the base layer reference picture and the enhancedlayer reference picture corresponding thereto may have the same pictureidentification information. The enhanced layer reference picture mayhave an image quality higher than that of the base layer referencepicture.

For example, when the current picture shown in FIG. 2 is the secondpicture 24 as well as a P picture, the reference picture of the secondpicture 24 is the first picture 22 and the second picture 24 is the keypicture. Accordingly, the second picture 24 which is the current picturecan be decoded by referring to the base layer reference picture or theenhanced layer reference picture of the first picture 22. At this time,the base layer reference picture and the enhanced layer referencepicture may have the same picture identification information and thepicture identification information may be the reference indexinformation or the picture number information of the reference picture.As another example, when the current picture is the fourth picture 28,the reference picture of the fourth picture 28 is the first and thirdpictures 22 and 26 and the fourth picture 28 corresponds to the non-keypicture. In this case, the reference picture of the fourth picture 28which is the current picture includes the base layer reference pictureof the first picture 22, the enhanced layer reference picture of thefirst picture 22 or the enhanced layer reference picture of the thirdpicture 26. The enhanced layer reference picture of the third picture 26indicates that the base layer reference picture of the third picture isalready reconstructed.

FIG. 4 is a flowchart illustrating a method for decoding a video signalaccording to another embodiment of the present invention.

First, a first reference picture can be obtained from a referencepicture list (S410). Here, the first reference picture is associatedwith the picture identification information and the pictureidentification information includes the reference index information orthe picture number information of the reference picture. For example,the first reference picture in the reference picture list can beobtained using the reference index information. A current block can bedecoded using the obtained first reference picture (S420). At this time,the first reference picture and a second reference picture correspondingthereto may have the same picture identification information and thefirst reference picture and the second reference picture aredistinguished from each other by another identification information. Forexample, the base layer reference picture 40 and the enhanced layerreference picture 42 having the same picture number may be distinguishedfrom each other by marking the base layer reference picture 40 with“base representation” in a decoded reference picture marking process.The first reference picture may belong to the base layer and the secondreference picture may belong to the enhanced layer. The enhanced layermay have image quality higher than that of the base layer. When thepicture including the current block is the key block, the referencepicture of the current block may be the first reference picture or thesecond reference picture corresponding thereto. The current block can bedecoded using the obtained reference picture.

As shown in FIGS. 3 and 4, when the reference picture is the firstpicture 22 or the second picture 24, which is the key picture, it ispossible to provide the base layer reference picture or the enhancedlayer reference picture to the current picture. Alternatively, it ispossible to provide the first reference picture or the second referencepicture to the current picture. Accordingly, the reference picture mustbe stored in the decoded picture buffer. According to the method fordecoding the video signal of the present invention, a method forallocating a reference number to the reference picture in the decodedpicture buffer or a method for managing the decoded picture buffer suchas a method for deleting the reference picture needs to be newlydefined. The method for managing the decoded picture buffer according toan embodiment of the present invention will be described in detail withreference to FIGS. 5 and 6.

First, in an embodiment of the present invention, when the referencepicture is the key picture, the same picture identification number maybe allocated to the base layer reference picture and the enhanced layerreference picture of the reference picture stored in the decoded picturebuffer. When the reference picture is the non-key picture, since theenhanced layer reference picture of the reference picture is stored inthe decoded picture buffer, one picture identification number isallocated to the enhanced layer reference picture of the referencepicture. That is, when the reference picture is the key picture, thebase layer reference picture and the enhanced layer reference picture ofthe reference picture may be treated as a virtual picture. Here, theallocated picture identification information includes the picture numberinformation or the reference index information and the picture numberinformation includes a long-term reference picture number.

FIG. 5 is a view illustrating a structure of a decoded picture bufferaccording to an embodiment of the present invention.

When the first picture 22 which is the key picture as well as thereference picture as shown in FIG. 2 is decoded and stored in thedecoded picture buffer, the base layer reference picture 40 and theenhanced layer reference picture 42 which configure the first picture 22are stored with a picture number “0”. In the second picture 24 which isthe key picture as well as the reference picture similar to the firstpicture 22, the base layer reference picture 44 and the enhanced layerreference picture 46 which configure the second picture 24 are storedwith a picture number “1”. In the third picture 26 which is the non-keypicture as well as the reference picture, the enhanced layer referencepicture 48 of the reference picture 26 is stored with a picture number“2”. The fifth pictures 32, 34, 36 and 38 are not stored in the decodedpicture buffer except for a case where the picture is not displayedimmediately after decoding, because the fifth pictures are non-referencepictures.

At this time, when the current picture is the key picture and refers tothe reference picture having the picture number “0”, since the baselayer reference picture 40 and the enhanced layer reference picture 42of the reference picture 22 have the same picture identificationinformation of the picture number “0”, the base layer reference picture40 and the enhanced layer reference picture 42 having the picture number“0” must be distinguished from each other. Accordingly, the presentinvention may use another identification information. For example, thebase layer reference picture 40 and the enhanced layer reference picture42 having the same picture number are distinguished from each other bymarking the base layer reference picture 40 with the “baserepresentation” in the decoded reference picture marking process.

As another embodiment of the present invention, the pictureidentification information of the pictures stored in the decoded picturebuffer varies depending on which picture is decoded in the decodedpicture buffer. Therefore, the first reference picture in the referencepicture list may be obtained from the reference picture list and thecurrent block may be decoded using the first reference picture. At thistime, the first reference picture and the second reference picturecorresponding thereto have the same picture identification informationand the first reference picture and the second reference picture may bedistinguished from each other by another identification information. Forexample, the first reference picture and the second reference picturehaving the same picture number may be distinguished from each other bymarking the first reference picture or the second reference picture withthe “base representation” in the decoded reference picture markingprocess. The first reference picture may belong to the base layer andthe second reference picture may belong to the enhanced layer. In thiscase, the first reference picture and the second reference picture maybe distinguished from each other by marking the first reference picturewith the “base representation”.

As another embodiment of the present invention, the reference picturelist may be initialized using the reference picture when decoding thecurrent block using the reference picture, as described with referenceto FIGS. 3 and 4. The initialized reference picture list may bereordered. When the reference picture list is reordered, the referencepicture can be obtained from the reordered reference picture list. Thereordering of the reference picture list will be described withreference to FIGS. 6 a and 6 b.

FIGS. 6 a to 6 b are views showing reordering of reference numbers of areference picture according to an embodiment of the present invention.

The reordering of the reference numbers represents a command forreallocating a lowest reference number to a picture having highestcorrelation with the current picture in the reference picture list andefficiently managing the reference picture when pictures, which aretemporally close to the current picture, have lower correlation with thecurrent picture than that of a picture, which is temporally far from thecurrent picture, when decoding the current picture. The reordering ofthe reference numbers will be described in detail with reference toFIGS. 6 a and 6 b.

FIG. 6 a shows the structure of the pictures in a state where the first,second, third and fourth pictures 22, 24, 26, 28 and 30 are decoded andstored in the decoded picture buffer. When the fifth picture 34 isdesired to be decoded, the reference picture list 0 of the picturesstored in the decoded picture buffer is configured as shown in FIG. 6 b.The reference numbers are given to the pictures while rotating thereference picture list 0 from the fifth picture 34 in a counterclockwisedirection and the reference numbers are given to the pictures whilerotating the reference picture list 1 from the fifth picture 34 in aclockwise direction. However, when the first picture 22, which istemporally far from the fifth picture 34, has higher correlation withthe fifth picture 34 than that of the fourth picture 28, which istemporally close to the fifth picture 34, in the reference picture list0, the reference number 0 is reallocated to the first picture 22 and thereference number 1 is reallocated to the fourth picture 28, therebyreordering the reference picture list. When the second picture 24, whichis temporally far from the fifth picture 34, has higher correlation withthe fifth picture 34 than that of the fourth picture 30, which istemporally close to the fifth picture 34, in the reference picture list1, the reference number 1 is reallocated to the second picture 24 andthe reference number 2 is reallocated to the fourth picture 30, therebyreordering the reference picture list.

In an embodiment of the present invention, as described above, in thereordering of the reference numbers, when the reference picture is thekey picture, the base layer reference picture and the enhanced layerreference picture are treated as one picture, to which the referencenumber is reallocated, and, when the reference picture is the non-keypicture, the reference number allocated to the enhanced layer referencepicture is reallocated, thereby reordering the reference picture list.

As another embodiment of the present invention, the initialization ofthe reference picture list uses the same method as that of thereordering of the reference numbers. For example, the pictureidentification information indicating the reference picture of thecurrent block is obtained and the reference picture stored in thereference picture buffer is read based on the obtained pictureidentification information. The current block is decoded using the readreference picture. The base layer reference picture and the enhancedlayer reference picture corresponding thereto may have the same pictureidentification information and the picture identification informationincludes the reference index information or the picture numberinformation of the reference picture. When the reference picture is thekey picture, the base layer reference picture and the enhanced layerreference picture of the reference picture are treated as one picture,to which the reference number may be allocated. When the referencepicture is a non-key picture, the reference number may be allocated tothe enhanced layer reference picture. Even when the reference pictureneeds to be no longer referred and is deleted from the decoded picturebuffer using a sliding window method, if the reference picture is thekey picture, the base layer reference picture and the enhanced layerreference picture of the reference picture are treated as one pictureand the reference picture may be deleted from the buffer. If thereference picture is the non-key picture, the enhanced layer referencepicture may be deleted from the buffer. In this case, the picture isdeleted using a first-in-first-out (FIFO) method for first deleting apicture which is first stored in the buffer.

As another embodiment of the present invention, a method for managing adecoded picture buffer using a memory management control operation MMCO(hereinafter, referred to as “MMCO”) will be described. When the MMCO isobtained from the current picture in a procedure for decoding thecurrent picture, the decoded picture buffer corresponding to the MMCO ismanaged. As shown in FIG. 5, when the current picture is the keypicture, both the base layer reference picture 52 and the enhanced layerreference picture 54 of the reference picture 50 in the decoded picturebuffer are subjected to a memory management control operation 56 (forexample, a command for moving the reference picture from a short-termmemory to a long-term memory). When the current picture is the non-keypicture, the enhanced layer reference picture of the reference picture58 in the decoded picture buffer is subjected to a memory managementcontrol operation 60. The management contents corresponding to the valueallocated to the MMCO will now be described in detail with reference toFIG. 7.

FIG. 7 is a view illustrating the management contents of the decodedpicture buffer corresponding to code numbers of the MMCO.

First, when the code number of the MMCO is 0, it is indicated that thememory management is finished. When the code number of the MMCO is 1, itis indicated that a short-term reference picture is marked with anon-reference picture. When the code number of the MMCO is 2, it isindicated that a long-term reference picture is marked with thenon-reference picture. When the code number of the MMCO is 3, it isindicated that the short-term reference picture is marked with thelong-term reference picture and moved to the long-term memory. When thecode number of the MMCO is 4, it is indicated that the size of thelong-term memory is decided. When the code number of the MMCO is 5, itis indicated that all the reference pictures are marked with thenon-reference picture and all the contents of the buffer are reset. Whenthe code number of the MMCO is 6, it is indicated that the currentpicture is marked with the long-term reference picture and moved to thelong-term memory.

The operation corresponding to the code number of the MMCO is performedwith respect to both the base layer reference picture and the enhancedlayer reference picture of the reference picture when the currentpicture is the key picture and is performed with respect to the enhancedlayer reference picture of the reference picture when the currentpicture is the non-key picture. That is, when the same pictureidentification number is given to the base layer reference picture andthe enhanced layer reference picture, the reordering of the referencenumber, the initialization of the reference picture list, the deletionof the reference picture and the management of the buffer using the MMCOmay be performed in the unit of the picture having the same pictureidentification number. The picture identification number includes thereference index information or the picture number information of thereference picture.

In another embodiment of the present invention, the pictureidentification information is allocated in the unit of the picturestored in the decoded picture buffer, regardless of whether thereference picture is the key picture or the non-key picture. That is,even when the reference picture is the key picture, different pictureidentification information is allocated to the base layer referencepicture and the enhanced layer reference picture of the referencepicture. When the reference picture is the non-key picture, the enhancedlayer reference picture of the reference picture is stored in thedecoded picture buffer and thus one piece of picture identificationinformation is allocated to the enhanced layer reference picture.

FIG. 8 is a view illustrating a structure of a decoded picture bufferaccording to another embodiment of the present invention.

When the first picture 22 (shown in FIG. 2) which is the key picture aswell as the reference picture is decoded and stored in the decodedpicture buffer, the picture number 0 is allocated to the base layerreference picture 40 of the first picture 22 and the picture number 1 isallocated to the enhanced layer reference picture 42 of the firstpicture 22. In the second picture 24 which is the key picture as well asthe reference picture similar to the first picture 22, the picturenumber 2 is allocated to the base layer reference picture 44 of thesecond picture 24 and the picture number 3 is allocated to the enhancedlayer reference picture 46 of the second picture 24. In the thirdpicture 26 which is the non-key picture as well as the referencepicture, since the enhanced layer reference picture is stored in thedecoded picture buffer, the picture number 4 is allocated to theenhanced layer reference picture 48. Since the fifth pictures 32, 34, 36and 38 are the non-reference picture, the fifth pictures are not storedin the decoded picture buffer except for the case that the fifthpictures are not displayed immediately after decoding.

As another embodiment of the present invention, in the reordering of thereference numbers, when the current picture is the key picture, only thereference number allocated to the base layer reference picture isreallocated, and, when the reference picture is the non-key picture,only the reference number allocated to the enhanced layer referencepicture is reallocated.

As another embodiment of the present invention, in the initialization ofthe reference picture list and the management of the buffer using theMMCO, if the current picture is the key picture, both the base layerreference picture and the enhanced layer reference picture of thereference picture are subjected to the initialization and the memorymanagement operation using the MMCO even when the reference numbersthereof are different, and, if the current picture is the non-keypicture, the enhanced layer reference picture of the reference pictureis subjected to the initialization and the memory management operationusing the MMCO.

As shown in FIG. 8, for example, an MMCO command 62 that the referencepicture 50 is moved from the short-term memory to the long-term memoryis obtained from the current picture. When the current picture is thekey picture, both the base layer reference picture 52 and the enhancedlayer reference picture 54 of the reference picture 50 are moved fromthe short-term memory to the long-term memory, and, when the currentpicture is the non-key picture, the enhanced layer reference picture 58of the reference picture is subjected to an MMCO command 64.

When the reference picture needs to be no longer referred and thus isdeleted from the decoded picture buffer using the sliding window method,if the current picture is the key picture, the base layer referencepicture and the enhanced layer reference picture of the referencepicture are deleted from the buffer even when the reference numbersthereof are different. However, if the current picture is the non-keypicture, the enhanced layer reference picture of the reference pictureis deleted from the buffer. In this case, the picture is deleted usingthe first-in-first-out (FIFO) method for first deleting a picture whichis first stored in the buffer.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, when a keypicture is decoded, a base layer reference picture or an enhanced layerreference picture of a reference picture are provided as the referencepicture, and, when a non-key picture is decoded, the enhanced layerreference picture of the reference picture is provided as the referencepicture. Accordingly, it is possible to minimize a problem caused in aprocedure for decoding a video signal due to transmission error. Whenthe video signal is decoded using the above decoding method, it ispossible to efficiently decode the video signal using a new method formanaging a decoded picture buffer which is optimized by the decodingmethod.

1. A method for decoding a video signal based on fine granularityscalability (FGS), the method comprising: a) obtaining a first referencepicture from a reference picture list; b) decoding a current block usingthe first reference picture, wherein the first reference picture and asecond reference picture corresponding thereto have same pictureidentification information and are distinguished from each other byanother identification information.
 2. The method of claim 1, wherein,when a picture including the current block is a key picture, thereference picture of the current block is the first reference picture orthe second reference picture corresponding thereto.
 3. The method ofclaim 1, wherein the first reference picture belongs to a base layer andthe second reference picture belongs to an enhanced layer.
 4. The methodof claim 3, wherein the enhanced layer has image quality higher thanthat of the base layer.
 5. The method of claim 1, further comprisinginitializing a reference picture list.
 6. The method of claim 5, furthercomprising reordering the initialized reference picture list.
 7. Themethod of claim 6, wherein the step a) is characterized by obtaining thefirst reference picture from the reordered reference picture list. 8.The method of claim 1, further comprising reading the first referencepicture in the reference picture list from a buffer based on the pictureidentification information.
 9. The method of claim 8, wherein thereference picture stored in the buffer is deleted from the buffer usinga predetermined buffer management method.
 10. The method of claim 9,wherein the predetermined buffer management method is an adaptive memorymanagement method or a sliding window method.
 11. The method of claim 1,wherein the picture identification information is reference indexinformation or picture number information of the reference picture.